Evaluation of localized thinning in straight carbon steel piping under internal pressure

The Scope of this paper is directed towards examining the influence of localized wall-thinning depth ratio and internal pressure on the collapse failure of some typical pressurized straight carbon steel pipes mainly used in refineries and petro-chemical plants. The investigation was achieved by conducting a parametric study using three-dimensional elastic-plastic finite element analysis (FEA). Several standard pipe sizes (NPS-4 to 14) with various wall thinning depth ratios (up to 75% of the wall thickness) have been considered. The localized wall thinning was assumed to be uniform. Based on the results, it was shown that the elastic-plastic FEA can be used to accurately estimate the “failure pressure” and assess the remaining strength of the pipe. In addition, the API 579 Fitness-For-Service assessment limiting pressure analysis has been considered as a basis to propose an API-modified simple way of assessing the integrity of pressurized locally thinned standard straight pipes.